The present invention is directed, in general, to communications networks, and, more specifically, to systems and methods for maintaining signaling links during outage periods in communications networks.
The world is currently experiencing revolutionary changes in communications systems, particularly in the area of wireless communications systems. At present, conventional wireless communications systems for general public use are terrestrial-based systems, such as a Global Service for Mobile (GSM) communications system. Advanced systems, however, utilize low earth orbit (LEO) and/or geo-stationary satellites. In addition to the use of satellites for voice transmissions, such satellites can also be used for the transmission of data and video.
A number of proposed broadband satellite systems will operate in the Ka (30 MHz) band. Such systems will be capable of transmitting several million bits per second and, thus, will support services such as the interconnection of remote Local Area Networks, or as an adjunct or alternative transmission path for Internet services.
A known problem in satellite communications networks is the vulnerability of an antenna, e.g. a satellite dish, to damage if the pointing angle is within a few degrees of the sun. For many terrestrial communications terminals, the pointing angle of its associated satellite dish to a satellite is within a few degrees of the angle to the sun for several minutes four times each year. When this occurs, the temperature in the satellite dish can reach a level that is harmful to its satellite transceiver. The only way to avoid such harmful temperature is to rotate the satellite dish away from its nominal pointing angle during the period(s) in which the sun angle is within a few degrees thereof. During this period, however, communications are lost between the terrestrial communications terminal and the satellite, as well as with any remote terminals that have established signaling links through the satellite to the terrestrial communications terminal associated with the satellite dish. When the satellite dish is returned to its nominal pointing angle, the signaling link to each of the remote terminals must be re-established. In some applications, there can be thousands of remote terminals, and the re-establishment of thousands of signaling links can put a tremendous strain on the signaling resources of the satellite communications network.
In addition to periods in which the sun can affect communications networks, other temporal periods during which a predetermined condition will affect communications can be identified prior to the occurrence thereof. Such xe2x80x9cconditionsxe2x80x9d can be related to system management, maintenance or repair. As in the case of sun outage, if system management, maintenance or repair processes require, or result in, the loss of many signaling links, the re-establishment of those signaling links can put a tremendous strain on the signaling resources of the communications network.
Accordingly, there is a need in the art for improved systems and methods for maintaining signaling links during outage periods in communications networks. Preferably, such systems and methods will eliminate the need to re-establish signaling links to each remote terminal following an outage period, and will utilize the existing hardware infrastructure associated with conventional communications networks, thereby reducing the cost of implementing such improved systems and methods.
To address the above-discussed deficiencies of the prior art, the present invention relates to systems and methods for maintaining signaling links during outage periods in communications networks. In the exemplary embodiments described hereinafter, periodic receiver ready frames are transmitted from a first terminal to a second terminal when there are no data frames to be transmitted. The periodic receiver ready frames maintain the signaling link between the terminals; e.g., if a receiver ready frame is not received within a predefined period, the connection will time out and the signaling link is lost. According to the principles of the present invention, a temporal period is determined during which a predetermined condition will affect communications with the second terminal; the predetermined condition can be, for example, a period during which the sun will be within a predetermined subtended angle of an antenna associated with the second terminal (in the prior art, all signaling links to a terminal would time out when the terminal""s associated satellite dish is rotated away from a pointing angle substantially directed towards the sun). The second terminal transmits a pause frame to the first terminal prior to the temporal period; the pause frame includes the identification of the temporal period. The first terminal then pauses the transmission of data frames and the periodic receiver ready frames during the temporal period, and resumes the transmission of data frames and periodic receiver ready frames subsequent to the expiration of the temporal period, whereby it is unnecessary to re-establish a signaling link between the first and second terminals upon the expiration of the temporal period.
In exemplary embodiments described herein, the pause frame can identify the temporal period by means of a start time value and a duration value, or by means of a start time value and an end time value. Typically, a protocol stack maintains and controls communications between terminals, and the pause frame can be transmitted, for example, over a Logical Link Control (LLC) layer of a signaling link protocol stack. Those skilled in the art are familiar with the nature and operation of a LLC, such as that defined by the IEEE 802.2 standard, incorporated herein by reference. The principles of the present invention are not limited, however, to the use of a particular protocol stack or standard, all such embodiments intended to be within the scope of the claims recited hereinafter.
In addition to pausing the transmission of receiver ready frames during the temporal period of outage, the first terminal can further store any received data frames destined for the second terminal in a buffer during the temporal period, and transmit the frames stored in the buffer upon the expiration of the temporal period. Alternatively, or in addition to buffering such data frames, the first terminal can transmit a message to the device or system that transmitted a data frame to inform it that communications with the second terminal are temporarily suspended.
The foregoing has outlined, rather broadly, the principles of the present invention so that those skilled in the art may better understand the detailed description of the exemplary embodiments that follow. Those skilled in the art should appreciate that they can readily use the disclosed conception and exemplary embodiments as a basis for designing or modifying other structures and methods for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form, as defined by the claims provided hereinafter.